Increased motor cortex excitability for concealed visual information

Deceptive behaviour involves complex neural processes involving the primary motor cortex. The dynamics of this motor cortex excitability prior to lying are still not well understood. We sought to examine whether corticospinal excitability can be used to suggest the presence of deliberately concealed information in a modified version of the Guilty Knowledge Test (GKT). Participants pressed keys to either truthfully or deceitfully indicate their familiarity with a series of faces. Motor-evoked-potentials (MEPs) were recorded during response preparation to measure muscle-specific neural excitability. We hypothesised that MEPs would increase during the deceptive condition not only in the lie-telling finger but also in the suppressed truth-telling finger. We report a group-level increase in overall corticospinal excitability 300 ms following stimulus onset during the deceptive condition, without specific activation of the neural representation of the truth-telling finger. We discuss cognitive processes, particularly response conflict and/or automated responses to familiar stimuli, which may drive the observed non-specific increase of motor excitability in deception

Az elektron lokalizáció hatása felületek és felületi nanostruktúrák elektronszerkezetére és mágneses tulajdonságaira = Effect of electron localization on the electronic and magnetic properties of surfaces and surface nanostructures

A kutatás során vizsgáltam fémes felületekre helyezett mágneses nano-részecskék mágneses anizotrópiáját, az atomok közötti kölcsönhatásokat. Megmutattuk, hogy a relativisztikus effektusoknak fontos szerepe van az alapállapot kialakulásában. Ebből a kutatásból négy folyóirat cikk készült. Vizsgáltuk atomi szennyezők vezetési tulajdonságait átlagtér és perturbatív közelítésben. Megmutattuk, hogy amíg az átlagtér közelítés gyakran hibás eredményt ad, addig a perturbáció számításból kapott eredmények sok esetben helyes eredményt adnak (ezen kutatásból két folyóirat cikk készült). Megmutattuk, hogy a felületi állapotok Rashba felhasadásának anizotrópiája megérthető az ú.n. kp-perturbáció számítás használatával (1 cikk). A DMFT+LDA módszer segítségével tanulmányoztuk a vanádium-dioxid elektronszerkezetének változását különböző rácstorzulások esetében (1 cikk). | n the present research project we studied the magnetic anisotropy of magnetic nano-structures and the interactions between them. We showed that the relativistic effects play a crucial role in the formation of the ground state. We published 4 journal articles from this research. We have studied the transport properties of quantum impurities by using mean-field and perturbative approximations. We showed that while the mean-field approximation often fails to serve a proper description the perturbative theory often captures the relevant physical properties (2 published papers). We served an explanation for the anisotropy of the Rashba splitting for surface states by using the so-called kp-perturbation theory. Applying the DMFT+LDA method we presented results for the influence of the lattice geometry on the electronic-structure of vanadium-dioxide (1 published paper)

Fluctuation-exchange approximation theory of the non-equilibrium singlet-triplet transition

As a continuation of a previous work [B. Horv\'ath et al., Phys. Rev. B {\bf 82}, 165129 (2010)], here we extend the so-called Fluctuation Exchange Approximation (FLEX) to study the non-equilibrium singlet-triplet transition. We show that, while being relatively fast and a conserving approximation, FLEX is able to recover all important features of the transition, including the evolution of the linear conductance throughout the transition, the two-stage Kondo effect on the triplet side, and the gradual opening of the singlet-triplet gap on the triplet side of the transition. A comparison with numerical renormalization group calculations also shows that FLEX captures rather well the width of the Kondo resonance. FLEX thus offers a viable route to describe correlated multi-level systems under non-equilibrium conditions, and, in its rather general form, as formulated here, it could find a broad application in molecular electronics calculations.Comment: 11 pages, 16 figures, new subsections adde

Failure of mean-field approach in out-of-equilibrium Anderson model

To explore the limitations of the mean field approximation, frequently used in \textit{ab initio} molecular electronics calculations, we study an out-of-equilibrium Anderson impurity model in a scattering formalism. We find regions in the parameter space where both magnetic and non-magnetic solutions are stable. We also observe a hysteresis in the non-equilibrium magnetization and current as a function of the applied bias voltage. The mean field method also predicts incorrectly local moment formation for large biases and a spin polarized current, and unphysical kinks appear in various physical quantities. The mean field approximation thus fails in every region where it predicts local moment formation.Comment: 5 pages, 5 figure

Non-equilibrium transport theory of the singlet-triplet transition: perturbative approach

We use a simple iterative perturbation theory to study the singlet-triplet (ST) transition in lateral and vertical quantum dots, modeled by the non-equilibrium two-level Anderson model. To a great surprise, the region of stable perturbation theory extends to relatively strong interactions, and this simple approach is able to reproduce all experimentally-observed features of the ST transition, including the formation of a dip in the differential conductance of a lateral dot indicative of the two-stage Kondo effect, or the maximum in the linear conductance around the transition point. Choosing the right starting point to the perturbation theory is, however, crucial to obtain reliable and meaningful results

Spin-polarized surface states close to adatoms on Cu(111)

We present a theoretical study of surface states close to 3d transition metal adatoms (Cr, Mn, Fe, Co, Ni and Cu) on a Cu(111) surface in terms of an embedding technique using the fully relativistic Korringa-Kohn-Rostoker method. For each of the adatoms we found resonances in the s-like states to be attributed to a localization of the surface states in the presence of an impurity. We studied the change of the s-like densities of states in the vicinity of the surface state band-edge due to scattering effects mediated via the adatom's d-orbitals. The obtained results show that a magnetic impurity causes spin-polarization of the surface states. In particular, the long-range oscillations of the spin-polarized s-like density of states around an Fe adatom are demonstrated.Comment: 5 pages, 5 figures, submitted to PR

Effects of strain on the electronic structure of VO_2

We present cluster-DMFT (CTQMC) calculations based on a downfolded tight-binding model in order to study the electronic structure of vanadium dioxide (VO_2) both in the low-temperature (M_1) and high-temperature (rutile) phases. Motivated by the recent efforts directed towards tuning the physical properties of VO_2 by depositing films on different supporting surfaces of different orientations we performed calculations for different geometries for both phases. In order to investigate the effects of the different growing geometries we applied both contraction and expansion for the lattice parameter along the rutile c-axis in the 3-dimensional translationally invariant systems miming the real situation. Our main focus is to identify the mechanisms governing the formation of the gap characterizing the M_1 phase and its dependence on strain. We found that the increase of the band-width with compression along the axis corresponding to the rutile c-axis is more important than the Peierls bonding-antibonding splitting